1. Field of the Invention
This invention relates to lithium haloboracites and to their use as solid electrolytes in galvanic cells.
2. Description of the Prior Art
Li has long been regarded as a desirable component of galvanic cells. Its unparalleled reduction potential (E.degree. .sub.red =-3.024v) and its light weight have often suggested its use as the anodic component in high energy-density batteries. Its reactivity with water has required the use of non-aqueous electrolytes such as organic-soluble lithium perchlorates, or fused lithium halides usable only at high temperature.
Solid electrolytes and in particular completely solid state galvanic cells offer special possibility for long shelf life, broad temperature limits of operability and miniaturization. The requirement for good ionic transport and very low electronic conductivity has led primarily to the use of various silver halides as solid electrolytes. The relatively low electrochemical potential of Ag/Ag+ and the relatively high density and cost are disadvantages. Alternatives to the solid state transport of Ag+ are the more recent discovery of transport by alkali metal cations in beta-aluminas and anion transport in calcia-stabilized zirconia at very high temperatures.
Two lithium haloboracites of the formula Li.sub.4 B.sub.7 O.sub.12 Cl and Li.sub.4 B.sub.7 O.sub.12 Br have been previously reported by Lavasseur et al. in Mater. Res. Bull. 6, 15-22 (1971); and by Jeitschko et al. in Z. Naturforsch, 27b, 1423 (Nov. 1972). They were described as related to the well-known boracites of divalent metals typified by the mineral boracite, Mg.sub.3 B.sub.7 O.sub.13 Cl. No mention is made of mixed halogen phases or electrical properties.